When a yarn spun in a pneumatic spinning apparatus or the like is wound on a package or the like, or when a bobbin is changed and re-winding is carried out, if a yarn being wound is broken, the splicing or knotting operation must be conducted. A slack tube is disposed to suck the yarn ends and eliminate yard slack during the splicing operation. However, since this slack tube continues the sucking action even when the splicing operation is not carried out, an unnecessary load is imposed on a sucking system.